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Immune · Evidence tier A

Thymosin alpha-1

thymalfasin (generic name) · Zadaxin (brand, SciClone Pharmaceuticals) · Tα1, Ta1, TA1 · thymosin alpha 1, thymosin α1 · thymosin alpha-1 acetate (salt form) · timosina alfa 1 (Italian name)

Thymosin alpha-1 is a lab-made copy of a natural peptide first found in the thymus, sold abroad as Zadaxin12. Large trials in sepsis and severe pancreatitis found no benefit, and US pharmacies may not make it345.

Last reviewed · First published · 55 sources · 33 min read · By the Pinc Peptide editors

Illustration: a glass vial with a pink label reading Thymosin alpha-1
Illustration, not a real product: an empty glass vial (photo: Missouri Historical Society, public domain) with our label. See every vial.

Quick answers

What is it?
A lab-made copy of a natural peptide, a chain of 28 amino acids first isolated from calf thymus1. It is thought to activate immune cells6. Other countries sell it as Zadaxin, mainly for hepatitis B and to boost flu shots67.
Does it work?
Not clearly. Large trials in sepsis (1,106 people), hepatitis C (552) and severe pancreatitis (508) found no benefit on their main goals348. Hepatitis B and COVID-19 trials disagree9101112; a 2026 review rated the hepatitis B evidence very uncertain13. We found no long COVID trial14.
Is it safe?
In trials it was usually well tolerated; injection-site irritation was the most common complaint6. Labels abroad warn about use in pregnancy, children, autoimmune disease and transplant patients6. We found no independent lab tests of gray-market vials15.
Is it legal?
It is not FDA-approved for any use6. US pharmacies may not make it, and an FDA advisory panel voted 17 to 4 against allowing it in 2024516. Italy sells it by prescription2. Sport does not ban it by name17.
What is in the vials?
Unknown. As of 5 October 2026 we found no independent lab tests of gray-market thymosin alpha-115. FDA doubted that the 3 mg/mL strength proposed for US pharmacies could even be dissolved6. Canada has seized vials sold under this name1819.

What it is

Thymosin alpha-1, generic name thymalfasin, is a chain of 28 amino acids whose first amino acid carries an acetyl cap2021. The same sequence forms the front end of a larger human protein, prothymosin alpha21. It is described as an immune modulator. Lab and animal studies suggest it activates dendritic cells (the cells that show germs to the rest of the immune system), partly through a sensor called toll-like receptor 9, raises natural killer cell activity and shifts helper T cells toward the type that fights viruses6. FDA notes that most of this comes from cell and animal work, often at much higher doses than people receive, so its relevance to humans is unclear6.

Goldstein and colleagues isolated thymosin alpha-1 from calf thymus and reported its sequence in 19771. From 1980, the US National Cancer Institute ran early trials at five institutions6. SciClone Pharmaceuticals markets a synthetic version as Zadaxin, and Italy’s medicines agency lists an authorization date of May 199627. In its 2014 annual report SciClone said Zadaxin was approved in over 30 countries, primarily China and countries in the Pacific Rim, Latin America, Eastern Europe and the Middle East, and that China supplied about 97% of its revenue in each year from 2012 to 20147. As of 5 October 2026, SciClone’s website still lists Zadaxin as a marketed product22.

Benefits: what the research shows

Thymosin alpha-1 has more human trial data than most gray-market peptides, but its large, well-run trials are mostly negative. In TESTS, a double-blind trial of 1,106 adults with sepsis at 22 hospitals in China, 28-day death rates were 23.4% with thymosin alpha-1 and 24.1% with placebo3. SciClone, the maker of Zadaxin, was a collaborator23. An earlier single-blind trial of 361 people with severe sepsis (ETASS) found 26.0% versus 35.0% deaths, a borderline result24. A 2025 pooled analysis of 11 sepsis trials found fewer deaths overall, but not when it was limited to higher-quality or multicenter trials25. In TRACE, a double-blind trial of 508 people with severe acute pancreatitis at 16 Chinese hospitals, it did not prevent infection of the damaged pancreas (15.7% versus 18.1% on placebo), and deaths did not differ4. A 2025 pooled analysis of TRACE and four smaller trials (706 people) reported fewer infections outside the pancreas (risk ratio 0.56), but these data came from only three of the trials, and hospital stays were not shorter26. In COVID-19, a 105-person double-blind trial in India reported fewer deaths only among severe cases, an open-label US pilot that analyzed 49 people found no significant difference in recovery, and two 2023 pooled analyses disagreed11122728. In an open-label US trial in 189 dialysis patients, an 8-week course to prevent COVID-19 was followed by 5 infections versus 7 without it, and 3 deaths versus 7, with no statistical tests posted2930. For hepatitis C, adding it to interferon treatment in 552 people did not raise cure rates (12.7% versus 10.5%)8. In hepatitis B, a 97-person placebo-controlled trial missed statistical significance (14% versus 4% complete response)10. A 98-person trial without placebo found more complete responses 18 months after a 26-week course (40.6% versus 9.4% untreated), but not after a 52-week course (26.5%), and response rates were similar when treatment ended9. An open-label trial in 690 people with hepatitis B and early (compensated) cirrhosis found that adding it to entecavir for 52 weeks did not change the combined rate of worsening liver disease, liver cancer or death over a median follow-up of 38.2 months31. A Cochrane review published 9 September 2026 pooled 10 hepatitis B trials (1,349 people, published 1991 to 2018). Deaths were lower with thymosin alpha-1 in pooled data from 3 trials (907 people; risk ratio 0.53), but the authors rated this evidence very low certainty and said they are not sure whether it reduces deaths13. FDA’s 2024 review concluded that the evidence did not support effectiveness for any of the 12 uses it examined6. Vaccine studies measured antibodies, not infections. In 85 analyzed older men given a 1986 flu shot, 69% on thymosin alpha-1 and 52% on placebo had a fourfold antibody rise; FDA called the results of this small, decades-old study questionable632. A 2012 pilot in 99 dialysis patients reported higher antibody levels at 3 weeks with 3.2 or 6.4 mg added to a pandemic flu vaccine, but levels then fell faster than with the vaccine alone, and FDA saw no lasting benefit633. In 488 people with advanced melanoma, adding it to chemotherapy gave more tumor responses, but longer survival (9.4 versus 6.6 months) was not statistically significant34. A trial in older adults getting COVID-19 boosters was still recruiting at its 16 July 2026 registry update35. We found no clinical trials in long COVID or chronic fatigue: FDA found no studies in chronic fatigue syndrome, and one 2023 lab study treated blood cells taken from people with long COVID61436. Animal studies report slower tumor growth and lower virus levels in mice, often at much higher doses than people receive6.

Key human studies

StudyDesignPeopleDose and routeResult
Wu et al., BMJ 2025 (TESTS)3PubMed · DOI · NCT02867267 Phase 3 randomized, double-blind, placebo-controlled trial at 22 hospitals in China; adults with sepsis 1,106 1.6 mg under the skin every 12 hours for 7 days 28-day death rate 23.4% vs 24.1% on placebo (hazard ratio 0.99, 95% CI 0.77 to 1.27); no secondary or safety outcome differed. Subgroups hinted at benefit at age 60 or older and worse survival under 603.
Ke et al., Intensive Care Med 2022 (TRACE)4PubMed · DOI · NCT02473406 Randomized, double-blind, placebo-controlled trial at 16 hospitals in China; adults 18 to 70 with predicted severe acute necrotizing pancreatitis 508 1.6 mg under the skin every 12 hours for 7 days, then once daily for 7 days Infected pancreatic necrosis during the hospital stay 15.7% vs 18.1% on placebo (difference -2.4 points, 95% CI -7.4 to 5.1; P = 0.48); 90-day deaths 9.1% in both groups; adverse events 8.3% vs 7.5%. SciClone supplied the drug4.
Ciancio et al., J Viral Hepat 20128PubMed · DOI · NCT01178996 Phase 3 randomized, double-blind, placebo-controlled trial; chronic hepatitis C not cured by earlier interferon and ribavirin 552 1.6 mg under the skin twice weekly for 48 weeks, added to peginterferon alfa-2a plus ribavirin Sustained cure 12.7% vs 10.5% on placebo (P = 0.407) in all randomized patients; 41.0% vs 26.3% (P = 0.048) among the 182 who completed 48 weeks. Side effects were similar8.
Wu et al., Crit Care 2013 (ETASS)24PubMed · DOI · NCT00711620 Randomized trial at 6 hospitals in China with saline placebo, patients blinded; severe sepsis 361 1.6 mg under the skin twice daily for 5 days, then once daily for 2 days 28-day death rate 26.0% vs 35.0% (relative risk 0.74, 95% CI 0.54 to 1.02; P = 0.062, log-rank P = 0.049). An immune-cell marker improved. No serious drug-related adverse events24.
Gravenstein et al., J Am Geriatr Soc 198932PubMed · DOI Randomized, double-blind, placebo-controlled trial; male veterans aged 65 to 99 given the 1986 flu vaccine 90 900 µg/m² under the skin twice weekly for 4 weeks (8 doses), starting right after vaccination Fourfold antibody rise in 31 of 45 (69%) vs 21 of 40 (52%) on placebo among the 85 analyzed. Antibody levels only; no infection outcomes. FDA said response rates were similar until 6 weeks after vaccination and called the study’s usefulness questionable632.
Tuthill et al., Int Immunopharmacol 2023 (preliminary report); final results on ClinicalTrials.gov, 202629PubMed · DOI · NCT04428008 Randomized, open-label pilot trial at five dialysis centers in Kansas City; prevention of COVID-19 versus standard care 189 1.6 mg under the skin twice weekly after dialysis for 8 weeks Within 6 months: COVID-19 in 5 of 91 vs 7 of 98; hospital stays 27 vs 26; other infections 8 vs 6; deaths 3 vs 7. No statistical tests were posted; the 2023 paper was an interim report2930.

Doses studied

Doses below are what studies used or what a label says. They are not advice, and gray-market products may not contain what their label says.

In human studies

Approved labels abroad: 1.6 mg under the skin twice weekly, 3 or 4 days apart, for 6 months (52 doses) for chronic hepatitis B (Indonesia); and one 1.6 mg vial, into muscle or under the skin, twice weekly for 4 weeks from the first flu shot, repeated from week 8 to week 12 (Italy)6. The most common trial dose was 1.6 mg under the skin, usually twice weekly, for up to 12 months6810. Sepsis and pancreatitis trials gave 1.6 mg every 12 hours for 7 days (followed in the pancreatitis trial by once daily for 7 more days), or twice daily for 5 days and then once daily for 2 days3424. COVID-19 trials gave 1.6 mg once daily, or 2 to 3 times daily, for 7 days6. Other studies used 0.8 mg six times a week for 2 weeks and then twice weekly in hepatitis B, 900 µg/m² twice weekly with a flu shot in older men, 3.2 or 6.4 mg with a pandemic flu vaccine, and up to 6.4 mg in melanoma632333452. Across trials, doses ranged from about 1 to 16 mg6. We found no human study of nasal sprays or of the 300 to 500 µg daily schedules common online.

In animal studies

Mice: 10 mg/kg under the skin twice daily for 7 days slowed lung tumor growth; 0.02 to 6 mg/kg twice daily for 7 days shrank melanoma tumors by 45 to 50% at every dose, with no dose-response; 6 mg/kg twice daily in a sepsis model gave only non-significant trends; 200 µg/kg a day into the abdominal cavity for 7 or 14 days lowered virus levels in a cytomegalovirus model; and 0.05 or 0.5 µg/kg daily for 4 days after a tetanus vaccine raised antibody levels by about 25 to 35%6. Rats: single IV doses of about 0.175 mg/kg in two blood-level studies6. These are animal research doses, not human doses.

What users report Anecdotal · not validated · not a recommendation

A peptide dosing website (published 1 March 2026, updated 28 September 2026) lists 300 to 500 µg injected under the skin once a day53.

Half-life
About 2 hours (means 1.8 to 2.6 hours)51Elimination half-life in 9 healthy volunteers after an under-the-skin dose of 900 µg/m² (1.6 to 2.2 mg), comparing Zadaxin with two other makers’ products. Blood levels peaked within about 2 hours, and 5 daily doses did not build up651. In rats given about 0.175 mg/kg IV, two studies found 1.9 and 3.0 hours6.
Routes
  • Subcutaneous injection (the approved route abroad; nearly all human data)
  • Intramuscular injection (allowed on the Italian label; used in early cancer trials)
  • Nasal spray (sold by some US clinics as 3 mg and 10 mg sprays; no human data found)
  • Intravenous injection (rat blood-level studies only)
  • Injection into the abdominal cavity (mouse studies only)

Every dose studied for Thymosin alpha-1, with sources →

Quality and the gray market

What testing finds

As of 5 October 2026, Finnrick’s thymosin alpha-1 page said “No published Thymosin Alpha 1 tests yet”, so we found no independent purity or dose data for gray-market vials15. FDA said the 2021 compounding nomination was unclear about which form it meant: its supplier certificate named one form in the title and gave the formula of the other6. That certificate listed a 98% purity result but no impurity tests, and FDA found no information on tests for microbes, bacterial toxins (endotoxin) or leftover solvents6. The nomination proposed a 3 mg/mL injection. FDA said the free peptide dissolves in water only up to about 2 mg/mL, and the acetate salt about 1 mg/mL, so that strength may not be possible; the products used abroad and in the trials it reviewed were 1.6 mg/mL6. Health Canada warns that unauthorized peptides may contain too much, too little or none of the active ingredient, or contaminants such as bacteria, endotoxins, heavy metals or glass particles49.

How it is sold

Thymosin alpha-1 is sold online as powder vials, for example 5 mg and 10 mg1953. As of 5 October 2026, Finnrick’s page listed 8 sellers, none tested, with prices from $1.32 to $24.00 per mg15. FDA’s 2024 review found US compounded 3 mg/mL injections; 3 mg and 10 mg nasal sprays sold by a naturopathic clinic, a holistic wellness center and an IV hydration lounge; and an “immune” bundle with zinc and vitamins6. It also found telemedicine, wellness-clinic and concierge websites saying they get it from compounding pharmacies, with claims for long COVID, chronic Lyme disease, chronic fatigue, mold illness, cancer, allergies and asthma6. In the UK, a peptide clinic’s website said thymosin alpha “boosts immune function” until the Guardian asked about it in April 202650. In 2025 Health Canada reported seizing it from a Calgary clinic and from online sellers, including vials labeled “PHX Labs Thymosin Alpha-1 10 MG”181948. We found no independent demand data, such as test-request counts or search trends.

Side effects and risks

  • Weak evidence of benefit: large trials found no benefit for survival, cure or infection prevention, so relying on it instead of proven treatment for an infection could cause harm3468.
  • Immune stimulation may be risky in people whose immune system is suppressed on purpose: the Indonesian label says not to use it in organ-transplant patients unless the benefits clearly outweigh the risks6. One of six stem-cell transplant patients in a pilot died of immune destruction of red blood cells; FDA said the role of thymosin alpha-1 is unclear654.
  • Labels abroad say not to use it in children or during pregnancy or breastfeeding, and to take care in people with allergies or autoimmune disease6.
  • In hepatitis B, temporary liver-enzyme flares occurred in 22 of 316 trial patients, and thyroid changes were reported when it was combined with interferon652.
  • Injected peptides can provoke immune reactions against themselves (immunogenicity). FDA flagged this risk, plus impurities and clumping, for compounded thymosin alpha-156.
  • FDA could not rule out unwanted interference with vaccine responses when it is given alongside vaccines6.
  • FDA found no published animal toxicity studies; the maker’s summaries report no safety signals, but the data are not public6. Daily use for months has had little testing: FDA’s review describes 600 µg a day for 10 weeks in 10 people with HIV and 1.6 mg a day for 16 weeks in 14 stem-cell transplant patients, neither with a comparison group6.
  • Gray-market vials have no independent test results that we found, and unauthorized peptides may be contaminated or mislabeled1549.
  • Legal risk: it is not FDA-approved, US pharmacies may not compound it, and Canada has seized it5618.

Documented harms

  • 30 Jul 2026FDA’s adverse event database (FAERS, via openFDA, data updated 30 July 2026) holds 203 reports that list thymalfasin, 185 of them from China and 9 from the US. 154 are coded serious, and thymalfasin is a suspect drug in 44. Reports are unverified and do not prove the drug caused the event55.
  • 20 Mar 2026A US consumer report received 20 March 2026 describes blurred vision, coded serious, in a 41-year-old woman injecting 0.4 mg a day under the skin for an immune disorder, alongside glutathione, vitamins, luteolin and palmitoylethanolamide55.
  • 24 Dec 2025Health Canada listed “PHX Labs Thymosin Alpha-1 10 MG” among unauthorized products sold online and seized at Rize Fitness in Vancouver19.
  • 1 Aug 2025Health Canada warned about unauthorized injectable peptides, including thymosin alpha, seized from and sold by Canada Peptide48.
  • 1 Apr 2025Health Canada seized unauthorized injectable peptides, including thymosin alpha-1, from the Optimum Wellness Centre in Calgary18.
  • 10 Jun 2024FDA’s search of US adverse event reports through 10 June 2024 found one relevant case: a 46-year-old man in a hepatitis C trial, also on peginterferon, was hospitalized for a day with atrial fibrillation, anxiety and a brief thyroid-hormone change. FDA said the peginterferon confounds the cause6.
  • Apr 2010In a pilot of 6 people given thymosin alpha-1 after half-matched stem-cell transplants, one developed fatal immune hemolytic anemia (immune destruction of red blood cells). FDA said it is unclear whether thymosin alpha-1 contributed654.
  • May 2005In a Japanese hepatitis B trial of 316 people, 22 had temporary liver-enzyme flares and 16 had treatment interrupted; all recovered without liver failure652.

Questions people ask

Is thymosin alpha-1 FDA approved?

No. FDA says it has approved no drug product containing thymosin alpha-16. It is a prescription drug in Italy, sold as Zadaxin, and its maker’s annual report for 2014 said it was approved in over 30 countries, including China27.

Is thymosin alpha-1 the same as TB-500?

No. Thymosin alpha-1 is a 28-amino-acid piece of the protein prothymosin alpha21. TB-500 is sold as a version of thymosin beta-4, a different protein; sport bans thymosin beta-4 and TB-500 by name but does not name thymosin alpha-117.

Does thymosin alpha-1 help long COVID?

We found no trial in people with long COVID. A 2023 lab study found it changed immune markers in blood cells taken from people with long COVID36. ClinicalTrials.gov listed no long COVID trial as of 5 October 2026, and FDA found no studies in chronic fatigue syndrome614.

Does thymosin alpha-1 work for sepsis?

A double-blind trial of 1,106 adults with sepsis (TESTS) found no difference in 28-day deaths (23.4% vs 24.1%)3. A smaller earlier trial and a 2025 pooled analysis suggested benefit, but the higher-quality trials in that analysis did not2425.

Is thymosin alpha-1 banned in sports?

It is not named on the World Anti-Doping Agency’s 2026 or 2027 Prohibited Lists1738. Because it is an approved drug in Italy, the catch-all ban on unapproved substances should not apply, by our reading2.

Can a US pharmacy compound thymosin alpha-1?

No. It is in no category of FDA’s pharmacy bulk-substance list, and FDA lists it among withdrawn nominations that may pose significant safety risks537. FDA’s advisory committee voted 17 to 4 against adding it in December 202416, and it was not on the committee’s July 2026 agenda44.

What is still unknown

  • Whether SciClone’s two US Phase 3 hepatitis C trials (NCT00039962, NCT00040027), registered in 2002, were ever published; the registry shows no results.
  • Current approval status outside Italy: SciClone’s ‘over 30 countries’ figure dates from 2014, and FDA could not verify it.
  • UK, Canadian and US state-level legal status beyond the seizures and warnings cited here was not verified.
  • No independent lab tests of gray-market thymosin alpha-1 were found as of 5 October 2026, so purity, dose accuracy and contamination are unknown.
  • Whether nasal sprays deliver any thymosin alpha-1 into the body; no human data were found.
  • Safety and effect of daily 300 to 500 µg schedules for weeks or months, as listed online; we found no trial that used them.
  • Results of NCT06821100 (thymalfasin with COVID-19 boosters in older adults), estimated to finish in December 2026.
  • Whether the full NCT04428008 dialysis results (posted 21 April 2026) will be analyzed statistically and published beyond the 2023 interim report.
  • No anti-doping agency statement on thymosin alpha-1 was found; the ‘not banned’ reading rests on the List text.
  • Whether it improves survival in hepatitis B-related acute-on-chronic liver failure: a 2026 report of an open-label trial (NCT03082885) claims better 90-day transplant-free survival, but its abstract gives no survival figures and describes 73 patients, while the registry lists 120 enrolled and no posted results.
  • Results of NCT05086614, a Phase 3 trial of thymosin alpha-1 after surgery for high-risk stage II and III colorectal cancer (Fudan University, 2,500 people planned), which was recruiting at our 5 October 2026 registry search.

Sources

  1. 1Thymosin alpha1: isolation and sequence analysis of an immunologically active thymic polypeptide Proceedings of the National Academy of Sciences, Feb 1977. pubmed.ncbi.nlm.nih.gov
  2. 2Banca Dati Farmaci: ZADAXIN (timosina alfa 1) 1.6 mg/ml powder and solvent for solution for injection, AIC 028364026 Agenzia Italiana del Farmaco (AIFA), accessed 5 Oct 2026. medicinali.aifa.gov.it
  3. 3The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial BMJ, 15 Jan 2025. pubmed.ncbi.nlm.nih.gov
  4. 4Immune enhancement in patients with predicted severe acute necrotising pancreatitis: a multicentre double-blind randomised controlled trial Intensive Care Medicine, Jul 2022. pubmed.ncbi.nlm.nih.gov
  5. 5Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks U.S. Food and Drug Administration, 22 Apr 2026. fda.gov
  6. 6FDA Evaluation of Thymosin Alpha-1 (Ta1)-Related Bulk Drug Substances (Ta1 free base and Ta1 acetate), briefing document for the Pharmacy Compounding Advisory Committee meeting of December 4, 2024 U.S. Food and Drug Administration, 15 Nov 2024. fda.gov
  7. 7SciClone Pharmaceuticals 2014 Annual Report (Form 10-K for fiscal 2014) SciClone Pharmaceuticals, Inc., 12 Mar 2015. annualreports.com
  8. 8Thymosin alpha-1 with peginterferon alfa-2a/ribavirin for chronic hepatitis C not responsive to IFN/ribavirin: an adjuvant role? Journal of Viral Hepatitis, Jan 2012. pubmed.ncbi.nlm.nih.gov
  9. 9Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial Hepatology, May 1998. pubmed.ncbi.nlm.nih.gov
  10. 10Thymosin alpha1 treatment of chronic hepatitis B: results of a phase III multicentre, randomized, double-blind and placebo-controlled study Journal of Viral Hepatitis, Sep 1999. pubmed.ncbi.nlm.nih.gov
  11. 11A Double-blind Multicenter Two-arm Randomized Placebo-controlled Phase-III Clinical Study to Evaluate the Effectiveness and Safety of Thymosin α1 as an Add-on Treatment to Existing Standard of Care Treatment in Moderate-to-severe COVID-19 Patients Indian Journal of Critical Care Medicine, Aug 2022. pubmed.ncbi.nlm.nih.gov
  12. 12A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection Journal of Infectious Diseases, 11 Jan 2023. pubmed.ncbi.nlm.nih.gov
  13. 13Thymosin-α1 for people with chronic hepatitis B Cochrane Database of Systematic Reviews, 9 Sep 2026. pubmed.ncbi.nlm.nih.gov
  14. 14ClinicalTrials.gov search: intervention ‘thymosin alpha’, condition ‘long COVID’ (0 studies) ClinicalTrials.gov, accessed 5 Oct 2026. clinicaltrials.gov
  15. 15Thymosin Alpha 1: safety testing results and vendor ratings Finnrick, accessed 5 Oct 2026. finnrick.com
  16. 16Final Summary Minutes of the Pharmacy Compounding Advisory Committee Meeting, December 4, 2024 U.S. Food and Drug Administration, 21 Feb 2025. fda.gov
  17. 17World Anti-Doping Code International Standard: Prohibited List 2026 World Anti-Doping Agency, 24 Sep 2025. wada-ama.org
  18. 18Unauthorized injectable peptide drugs seized from Optimum Wellness Centre in Calgary, Alberta may pose serious health risks (RA-77218) Health Canada, 1 Apr 2025. recalls-rappels.canada.ca
  19. 19Unauthorized health products sold online and seized at Rize Fitness may pose serious health risks (RA-81403) Health Canada, 24 Dec 2025. recalls-rappels.canada.ca
  20. 20Thymalfasin, PubChem compound summary (CID 16130571) PubChem, U.S. National Library of Medicine, accessed 5 Oct 2026. pubchem.ncbi.nlm.nih.gov
  21. 21UniProtKB P06454: Prothymosin alpha (human), with the thymosin alpha-1 peptide at residues 2 to 29 UniProt Consortium, 2 Sep 2026. uniprot.org
  22. 22SciClone Pharmaceuticals (Holdings) Limited: home page, marketed products (Zadaxin, thymalfasin) SciClone Pharmaceuticals (Holdings) Limited, accessed 5 Oct 2026. sciclone.com
  23. 23NCT02867267: The Efficacy and Safety of Ta1 for Sepsis (TESTS) ClinicalTrials.gov, 10 Apr 2023. clinicaltrials.gov
  24. 24The efficacy of thymosin alpha 1 for severe sepsis (ETASS): a multicenter, single-blind, randomized and controlled trial Critical Care, 17 Jan 2013. pubmed.ncbi.nlm.nih.gov
  25. 25Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials Frontiers in Cellular and Infection Microbiology, 2025. pubmed.ncbi.nlm.nih.gov
  26. 26Thymosin alpha 1 alleviates inflammation and prevents infection in patients with severe acute pancreatitis through immune regulation: a systematic review and meta-analysis Frontiers in Immunology, 2025. pubmed.ncbi.nlm.nih.gov
  27. 27Thymosin alpha1 use in adult COVID-19 patients: A systematic review and meta-analysis on clinical outcomes International Immunopharmacology, Jan 2023. pubmed.ncbi.nlm.nih.gov
  28. 28The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression Inflammopharmacology, Dec 2023. pubmed.ncbi.nlm.nih.gov
  29. 29NCT04428008: Thymosin Alpha 1 to Prevent COVID-19 Infection in Renal Dialysis Patients (results posted 21 April 2026) ClinicalTrials.gov, 21 Apr 2026. clinicaltrials.gov
  30. 30A pilot trial of Thymalfasin (Ta1) to prevent covid-19 infection and morbidities in renal dialysis patients: Preliminary report International Immunopharmacology, Apr 2023. pubmed.ncbi.nlm.nih.gov
  31. 31Combination of entecavir with thymosin alpha-1 in HBV-related compensated cirrhosis: a prospective multicenter randomized open-label study Expert Opinion on Biological Therapy, Jul 2018. pubmed.ncbi.nlm.nih.gov
  32. 32Augmentation of influenza antibody response in elderly men by thymosin alpha one. A double-blind placebo-controlled clinical study Journal of the American Geriatrics Society, Jan 1989. pubmed.ncbi.nlm.nih.gov
  33. 33Thymosin-alpha 1 (Zadaxin) enhances the immunogenicity of an adjuvated pandemic H1N1v influenza vaccine (Focetria) in hemodialyzed patients: a pilot study Vaccine, 1 Feb 2012. pubmed.ncbi.nlm.nih.gov
  34. 34Large randomized study of thymosin alpha 1, interferon alfa, or both in combination with dacarbazine in patients with metastatic melanoma Journal of Clinical Oncology, 1 Apr 2010. pubmed.ncbi.nlm.nih.gov
  35. 35NCT06821100: Thymalfasin (Thymosin Alpha 1; Ta1) as an Enhancer of Vaccine Response Among Older Adults Receiving Booster Doses of COVID-19 Vaccine ClinicalTrials.gov, 16 Jul 2026. clinicaltrials.gov
  36. 36Thymosin alpha 1 restores the immune homeostasis in lymphocytes during Post-Acute sequelae of SARS-CoV-2 infection International Immunopharmacology, May 2023. pubmed.ncbi.nlm.nih.gov
  37. 37Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act (categories list) U.S. Food and Drug Administration, 14 May 2026. fda.gov
  38. 38World Anti-Doping Code International Standard: Prohibited List 2027 World Anti-Doping Agency, 21 Sep 2026. wada-ama.org
  39. 39Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026 (F2026L01327) Federal Register of Legislation, Australian Government, 28 Sep 2026. legislation.gov.au
  40. 40NCT00039962: Thymosin Plus PEG-Interferon in Hepatitis C Patients With Cirrhosis Who Did Not Respond to Interferon or Interferon Plus Ribavirin ClinicalTrials.gov, 15 Jan 2008. clinicaltrials.gov
  41. 41NCT00040027: Thymosin Plus PEG-Interferon in Non-Cirrhotic Hepatitis C Patients Who Did Not Respond to Interferon or Interferon Plus Ribavirin ClinicalTrials.gov, 15 Jan 2008. clinicaltrials.gov
  42. 42Nomination from Wells Pharmacy Network (thymosin alpha-1), document FDA-2015-N-3534-0288 Regulations.gov (U.S. Food and Drug Administration docket FDA-2015-N-3534), 26 Feb 2021. regulations.gov
  43. 43Withdrawal from Wells Pharmacy Network (CJC-1295 and thymosin alpha 1 nominations), document FDA-2015-N-3534-0470 Regulations.gov (U.S. Food and Drug Administration docket FDA-2015-N-3534), 19 Sep 2024. regulations.gov
  44. 44July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee U.S. Food and Drug Administration, 6 Aug 2026. fda.gov
  45. 45Warning letter to Advanced Nutriceuticals, LLC dba The Guyer Institute of Molecular Medicine (MARCS-CMS 615908) U.S. Food and Drug Administration, 10 Nov 2021. fda.gov
  46. 46Bulk Drug Substances Nominated for Use in Compounding Under Section 503B of the Federal Food, Drug, and Cosmetic Act (categories list) U.S. Food and Drug Administration, 21 Mar 2025. fda.gov
  47. 47EU/3/02/110: orphan designation for treatment of hepatocellular carcinoma (thymalfasin) European Medicines Agency, 8 Jan 2003. ema.europa.eu
  48. 48Unauthorized injectable peptide drugs seized and sold by Canada Peptide may pose serious health risks (RA-77807) Health Canada, 1 Aug 2025. recalls-rappels.canada.ca
  49. 49Think twice before injecting peptides bought online: unauthorized products can seriously harm you (RA-81874) Health Canada, 9 Apr 2026. recalls-rappels.canada.ca
  50. 50Medicines watchdog to investigate UK peptide clinics over health claims The Guardian, 4 Apr 2026. theguardian.com
  51. 51Pharmacokinetics of thymosin alpha1 after subcutaneous injection of three different formulations in healthy volunteers International Journal of Clinical Pharmacology and Therapeutics, Jan 1999. pubmed.ncbi.nlm.nih.gov
  52. 52The efficacy and safety of thymosin alpha-1 in Japanese patients with chronic hepatitis B; results from a randomized clinical trial Journal of Viral Hepatitis, May 2005. pubmed.ncbi.nlm.nih.gov
  53. 53Thymosin Alpha-1 Dosage: 5 mg Vial (published 1 March 2026, updated 28 September 2026) PeptideDosages, 28 Sep 2026. peptidedosages.com
  54. 54Thymosin alpha1 to harness immunity to pathogens after haploidentical hematopoietic transplantation Annals of the New York Academy of Sciences, Apr 2010. pubmed.ncbi.nlm.nih.gov
  55. 55FDA Adverse Event Reporting System (FAERS) reports listing thymalfasin as an active substance, retrieved via the openFDA drug/event API U.S. Food and Drug Administration (openFDA), 30 Jul 2026. api.fda.gov · data query

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